The present invention relates to semiconductor detector devices for position-sensitive detection of sparse events.
Semiconductor detector devices are devices that use a layer of semiconductor material to generate charge in response to an input event, and then collect the charge to provide detection of that event. Position-sensitivity of the detection may be provided by collecting the charge in an array of pixels. This allows the positions of events to be determined on the basis of the position of the pixels that collect the charge. In many cases the events are relatively sparse so that only one or a small number of events occur simultaneously, and this allows the design of the semiconductor detector device to be simplified.
Two main types of semiconductor detector device are known that may be used to detect sparse events, namely an active pixel detector device or a strip detector device.
In an active pixel detector device, the pixels are arranged to be operated in a voltaic mode in which the charge is collected on the pixel and periodically read out. In this case, each pixel comprises an arrangement of active devices integrated with the layer of semiconductor material, for example with a CMOS (complimentary metal-oxide-semiconductor) construction. Typically, the active devices include a buffer device arrangement arranged to buffer a signal representative of the charge collected by the pixel and a sampling device arrangement that allows the buffered signal to be read out onto tracks connected to the pixels. The sampling device arrangements of the pixels are then selectively activated to read out the signals. In this manner, the pixels are scanned, for example by selectively activating rows of pixels to read out the signals simultaneously for the pixels in each column that are connected to the same track. The position of a detected event is determined from the row currently being sampled and the column of the track on which the signal appears.
An active pixel detector device is commonly used for applications requiring continuous detection of multiple events, for example in an image sensor in which events across the entire array are simultaneously detected. An active pixel detector device may also be used to detect sparse events, but in that case suffers from the disadvantage of having a relatively low detection bandwidth as the readout time is shared between multiple pixels as the array is scanned. Furthermore, there are disadvantages in the construction. The scanning of the array of pixels introduces complexity into the design of the control circuit to provide the addressing of individual pixels. The design and the construction of the arrangement of active devices in each pixel are also complex.
A strip detector device is a type of device that avoids some of these limitations of active pixel detector device. In particular, the layer of semiconductor material is arranged to be operated in a conductive mode in which the collected charge is continuously detected by contacts arranged as an array of parallel strips on each side of the layer of semiconductor material extending at an angle to each other, typically perpendicular. An event generates charge that is simultaneously collected by contacts on each side of the semiconducting material. The position of a detected event is determined from the overlap between the strips, due to the perpendicular crossing arrangement of the array of strips.
A strip detector device may be used to detect sparse events, including events that are sufficiently separated in time, and in some arrangements a limited number of simultaneous events that may be discriminated on the basis of a characteristic of the detected signal. However, a strip detector device has the disadvantage of requiring contacts to be provided on both sides of the layer of semiconductor material, which creates difficulties both in forming the contacts themselves and providing connections to both sides. This prohibits the use of some manufacturing techniques and even where possible increases manufacturing costs. Formation of contacts on both sides of the layer of semiconductor material also limits the possibility of integrating additional devices into the layer of semiconductor material for example using a CMOS construction.
It would be desirable to provide a semiconductor detector device that may be used to provide position-sensitive detection of sparse events but in which at least some of the above described difficulties with an active pixel detector device or a strip detector device are alleviated.